How can I tell whether my child has food poisoning?

Food poisoning, which is usually caused by eating food or drinking water that's contaminated with one of several kinds of nasty bacteria, can be hard to distinguish from a stomach virus, which is usually picked up on the hands and transferred to the mouth. The symptoms are the same: abdominal cramping, vomiting, diarrhea, and often fever, chills, achiness, and headache.

If your child has food poisoning, the symptoms will likely appear two to 48 hours after eating the food and will usually last a day or two, but can continue in severe cases for a week or more.

How can I tell what kind of food poisoning my child has?

Testing of blood, stool, and leftover food may identify the bacteria when necessary, but often the doctor won't need to identify the exact culprit because the treatment is the same regardless. (In fact, the treatment is the same for a stomach virus, too.) There are exceptions, though. If there's blood in your child's stool, for example, the doctor will test to make sure that he doesn't have food poisoning that's caused by a potentially dangerous bacteria, like E.coli 0157:H7, Shigella, or Salmonella.

According to the Centers for Disease Control and Prevention (CDC), the most common food-borne infections are those caused by the bacteria Campylobacter, Salmonella, and E.coli 0157:H7, as well as by a group of viruses called noroviruses. Less common — but dangerous if left untreated — is botulism. Here's a quick look at these bacteria:

Campylobacter is the most frequently diagnosed food-borne bacterium. It's usually transmitted through raw or undercooked poultry or unpasteurized milk, but your child can also get it from contaminated water. It's not usually spread from person to person, but it can be. (If your child has it and has diarrhea, for example, you could possibly get it from cleaning him up.)

It's also possible to contract the bacteria from the stool of a dog or cat. Campylobacter often goes undiagnosed because there are sometimes no symptoms, but signs can include nausea and vomiting, diarrhea (sometimes bloody), cramping, abdominal pain, and fever. It usually lasts for two to five days, but can linger for up to ten days.

Salmonella can be present in raw or undercooked eggs, poultry and meat, raw milk and dairy products, and seafood, and can be spread by food handlers. Reptiles like pet iguanas, turtles, lizards, and snakes can also carry salmonella. In most cases, if your child has a bout of salmonella, he'll develop fever, diarrhea, and abdominal cramps. He may also have tiny pink spots on his skin.

Symptoms usually start eight to 48 hours after contact and last for a day or two, though they can persist for more than a week, and the bacteria can continue to exist in the body for months. Two-thirds of patients with salmonella are under 20 years old. In a person with a compromised immune system, salmonella can invade the bloodstream and become life threatening.

E. coli is transmitted through food or water that's contaminated with microscopic amounts of cow feces. (If a person has E. coli and doesn't wash her hands after using the toilet, she can also spread it to another person.) E. coli can cause severe, sometimes bloody diarrhea and painful abdominal cramps, without much of a fever.

There are a number of strains of Escherichia coli. E. coli 0157:H7 is a particular strain that causes a more severe, longer-lasting illness. In babies and children, E. coli 0157:H7 can be life threatening and often requires hospitalization. Symptoms can begin eight to 48 hours after your child eats a food contaminated with the bacteria and last about two to five days.

Norovirus is also called Norwalk-like virus (NLVs) or calicivirus, because it belongs to the Caliciviridae virus family. This very common virus isn't often diagnosed because a lab test for it isn't widely available. Severe vomiting is the hallmark sign, and it usually begins suddenly, about 24 to 48 hours after contact with the virus, although symptoms can show up as early as 12 hours after contact.

A norovirus is transmitted through contaminated food, utensils, and surfaces. Because it's highly contagious, it spreads easily in daycare facilities and homes. There are many strains of norovirus, so it's hard to develop immunity to them. A case of norovirus usually goes away on its own in one to two days, but in the meantime you'll want to make sure that your child doesn't get dehydrated because of the vomiting.

Botulism is fairly rare — there are only about 110 cases in the United States each year. It's caused by the bacteria Clostridium botulinum, which is found in soil. But it's most often transmitted through improperly canned or preserved food, especially home-canned vegetables, cured pork and ham, smoked or raw fish, honey, and corn syrup.

Infant botulism happens when a baby eats the bacteria or its spores, and they then grow in his intestinal tract. (This is why you should never feed honey to a baby under age 1.) Symptoms of botulism include constipation, weakness, droopy eyelids, and difficulty swallowing. (The child will be alert, though, despite his weakness.) Left untreated, botulism can progress to muscle and respiratory paralysis. The symptoms usually show up in eight to 36 hours.

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